摘要:

Catecholamines restore cardiac contraction depressed by hyperkalaemia (raised [K+]o) and acidosis, yet in exercise hyperkalaemia and acidosis are tolerated during βadrenergic blockade. To test whether the negative effects of raised [K+]oare offset by a non‐adrenergic hormone, angiotensin II (AII) was given to rabbit papillary muscle (AII 75 nm,n=9) and rabbit isolated working hearts (AII 5 nm,n=8) perfused with 8 and 10 mmK+Tyrode at 37 °C. A similar protocol was also performed in a further nine isolated hearts treated with propranolol (1 μm) and prazosin (1 μm). AII caused a significant (P<0.01) increases in contraction and aortic flow in normal Tyrode and maintained aortic flow during high [K+]o. In the papillary muscle and isolated heart treated with adrenergic blockers, high [K+]oreduced the stimulatory effects of AII, but contraction and aortic flow was still significantly greater (P<0.01) than in high [K+]oalone. These results show that AII can ameliorate the depressive effects of high [K+]oon the heart. The local release of AII in the heart during activation of the sympathetic nervous system and the rise in circulating AII during exercise could therefore play a role in protecting the heart from hyperkal

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.453213000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Neural control of the circulation during static two‐leg exercise was evaluated in 10 subjects. External compression of the legs was employed to assess muscle mechano‐receptor influence by achieving the same intramuscular pressure (80 mmHg) as developed during exercise. The muscle metabo‐reflex contribution was assessed by post‐exercise muscle ischaemia, and the influence from higher centres in the central nervous system (‘central command’) was taken as the part of the response that could not be accounted for by the two reflex contributions. During static exercise, mean arterial pressure was higher (26±3 mmHg;P<0.01) as compared with leg compression (10±2 mmHg) and with post‐exercise muscle ischaemia (11±2 mmHg). Heart rate (25±4 b.p.m.) and cardiac output (0.8±0.3 L min‐1) were increased only during static exercise (P<0.05). Increase in total peripheral resistance were similar during static exercise, post‐exercise muscle ischaemia and leg compression. The pressor response to static exercise with a large muscle group was equally attributable to mechanical and metabolic stimulation of afferent nerves; and the two influences were redundant in their effect on total peripheral resistance. In contrast, the influence from central command was directed to the heart with elevation of its

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.472186000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The vibration sensitivity of feline muscle spindle endings is known to vary as a result of preceding muscle conditioning manoeuvres. If similar after‐effects occur in man they should be expected to influence the strength of the tonic vibration reflex (TVR). To study this issue, vibration was applied over the finger extensor tendons of 11 volunteers who actively held their fingers in a semi‐extended position. The TVR, measured as electromyographic responses and angular deflections at the metacarpophalangeal joints, was found to be stronger when the extensors prior to the test had been contracted in a shortened position than when they had been contracted in a stretched position. This difference was reduced when the vibration stimulus was preceded by a strong extensor contraction in the test position. The antigravity extensor EMG activity required to keep the fingers in the test position was weaker when the conditioning contraction was performed at a short muscle length than when it was performed at a long muscle length. The variations in magnitude of the TVR can be attributed to ‘thixotropic’ properties of intrafusal muscle fibres, resulting in a slack following conditioning at a long muscle length. The different EMG levels required for position holding can be explained by similar properties of extrafusal muscle fibres. In conclusion, the results demonstrate the importance of taking the ‘history of movement’ into account in the design of all

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.465180000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of the calmodulin‐inhibitors trifluoperazine, thioridazine and zaldaride maleate on the responses to electrical stimulation in isolated frog skeletal muscle fibres were investigated. All three drugs initially reduced the amplitude of the action potentials but potentiated twitch force. This was followed by a total loss of action potentials and force production. However, the resting membrane potential was not changed. The effects were completely reversible upon removal of the drugs. These results suggest that an intact calmodulin system is required for normal function of the sarcolemmal sodium channels of frog skeletal muscl

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.466181000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of perchlorate (1–20 mm) on myofibrillar calcium responsiveness have been tested in Triton X‐100‐skinned fibre bundles from rat soleus (slow‐twitch) and extensor digitorum longus (fast‐twitch) skeletal muscles. In extensor digitorum longus and soleus, perchlorate dose‐dependently shifted the pCa (‐log[Ca2+])/tension relationship towards lower free calcium concentration (sensitizing effect) and maximal tension was unchanged. The degree of sensitization was greater in extensor digitorum longus than in soleus bundles. Reversibility after exposure to 12 mmperchlorate was complete in soleus but not in extensor digitorum longus muscles. In fact, the ‘return’ pCa/tension relationship in extensor digitorum longus was shifted to higher free calcium concentration (desensitizing effect) compared with control. Perchlorate (12 mm) also enhanced myofibrillar calcium responsiveness of frog semitendinosus skinned skeletal fibres. Assuming a passive distribution of perchlorate across the sarcolemma, this sensitizing effect is probably not involved in perchlorate‐induced potentiation of contractile responses of intact muscles and thereby supports the specificity of perchlorate as an agonist of the excitation/calcium release sequence in ske

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.183000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The separate effects of 18 weeks of intensive strength and endurance training on isometric knee extension (KE) and flexion (KF) strength and walking speed were studied in 76‐to 78‐year‐old women. Maximal voluntary isometric force for both KE and KF was measured in a sitting position on a custom‐made dynamometer chair at a knee angle of 60° from full extension. Maximal walking speed was measured over a distance of 10 m. The endurance‐trained women increased KE torque and KE torque/body mass after the first 9 weeks of training when compared with the controls. When comparing the baseline, 9 week and 18 week measurements within the groups separately, both the endurance‐ and strength‐training groups increased KE torque, KE torque/body mass and walking speed. Individual changes in KE torque/body mass before and after 18 weeks of training averaged 19.1% in the strength group, 30.9% in the endurance group and 2.0% in the controls. This study indicates that in elderly women the effects of physical training on muscle strength and walking speed occur after endurance as well as strength training. The considerable interindividual variation in change of muscle performance is also

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.461177000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Physical training increases insulin stimulated glucose uptake in adipocytes and decreases insulin secretion from pancreatic islets. The mechanism behind these adaptations is not known. Because in acute exercise adrenergic activity influences both adipocytes and pancreatic islets, the sympathetic nervous system was examined as the possible mediator. Rats were either adrenodemedullated or sham adrenodemedullated and underwent either unilateral abdominal sympathectomy or were sham sympathectomized. Resting plasma adrenaline concentration in adrenodemedullated rats was 32% of the concentration in sham adrenodemedullated rats (P<0.0001) and muscle noradrenaline content in sympathectomized leg was 9% of content in sham sympathectomized leg (P<0.0001). After operations rats were either swim trained for 10 weeks or remained sedentary. Insulin stimulated 3‐O‐[14C]methylglucose transport was measured in adipocytes from epididymal fat pads, and insulin secretion and glucose metabolism were measured in glucose stimulated pancreatic islets. Training increased insulin stimulated glucose transport in adipocytes (P<0.0001) and decreased their size (P<0.0001), but neither adrenodemedullation nor sympathetic denervation affected these parameters significantly. Training decreased insulin secretion (P<0.01) and increased glucose oxidation (P=0.02) and utilization (P=0.08) in pancreatic islets, but none of these parameters was affected significantly by adrenodemedullation. It is concluded that adrenergic activity is not important for the training induced decrease in size and increase in insulin stimulated glucose transport of adipocytes. Neither is an intact adrenal medulla necessary for training‐induced adaptations in pancreatic beta cell function. Finally, in response to training, β cell insulin secretion and glucose metabolism changed in opposite dire

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.462214000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Isovolumetric contractions were induced electrically in five guinea‐pig bladders in a 1.8 mmCa2+buffer solution at two different volumes. The rate of pressure development was studied by analysis of phase‐plots, which are plots of the rate of change of intravesical pressure as a function of pressure. At relatively large volumes the rate of pressure development showed a biphasic nature, suggesting that two different processes were involved in different phases of contraction. Extracellular Ca2+was manipulated to identify these processes. Removal of extracellular Ca2+led to an 85% reduction of the maximum isovolumetric pressure in subsequent stimulations, but pressure developed faster. The biphasic nature of pressure development at large volumes tended to disappear. It was concluded that at large bladder volumes pressure development in this type of smooth muscle is determined by the release of intracellularly stored Ca2+in the early phase of contraction. In the final phase the rate of pressure development is limited by the extracellular Ca2+influx. At small bladder volumes the Ca2+influx takes place at a higher rate, so that the contribution of intracellular Ca2+release to pressure development could not be identified at these volu

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.463178000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Shortening induced deactivation, the depressant effect of active muscle shortening on the subsequently measured isometric force, has been shown in smooth muscle strips and rings. The guinea‐pig bladder permits the investigation of this phenomenon in a whole organ preparation. Previous work in our laboratory showed that shortening of thein vitroguinea‐pig detrusor muscle had a depressant effect on the isovolumetric pressure that could be generated immediately afterwards. To test the hypothesis that this was caused by deactivation, the effects of active and passive detrusor shortening on the subsequently measured isovolumetric pressure were compared. The isovolumetric pressures measured after 5 min periods of recovery were taken as control values. It was found that the isovolumetric pressure after passive shortening was 7% smaller than the isovolumetric pressure without preceding shortening. This difference was ascribed to viscoelastic relaxation during shortening. Active shortening had an additional 8% depressant effect on isovolumetric pressure compared with passive shortening. The effects of active and passive shortening differed significantly. It was concluded that shortening induced deactivation in the guinea‐pig urinary bladder smooth musclein totocan be considered proven. The fact that deactivation is shown both by striated and smooth muscle preparations is in line with the assumption that it is caused by reduced actin‐myosin interaction. The hypothesis that (in striated muscle) the latter is effected by a decrease in troponin–calcium binding, however, needs recons

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.464179000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The occurrence of inflammation as indicated by extravasation of Evans blue bound to plasma proteins was examined in various parts of the gastrointestinal tract in the rat, following administration of tachykinins, capsaicin and hydrochloric acid. Intravenous neurokinin A dose‐dependently induced extravasation in stomach, duodenum, jejunum, caecum and colon, but had no effect in ileum. Neurokinin B equipotently induced extravasation in the stomach but had no effect in other parts of the gut and substance P had no effects on extravasation of Evans blue in any of the examined parts of the gastrointestinal tract. Capsaicin given intraperitoneally increased vascular permeability in stomach and duodenum only, while extravasation of Evans blue after capsaicin given intraluminally did not differ from the effect of the vehicle alone. As a comparison, HCl given intraluminally in the duodenum was found to induce a prominent extravasation of Evans blue of a greater magnitude than that of tachykinins. We suggest that tachykinins, and in particular neurokinin A, may be of importance for extravasation of plasma proteins as part of inflammatory reactions in the upper and lower gastrointestinal trac

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.457174000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY